Planar displays such as CRTs, LCD panels, laser scan and projection screens are well-known. These displays present an image at a fixed focal length from the audience. The appearance of three-dimensionality is a visual effect created by perspective, shading and occlusion and motion parallax. Integral photographic displays and lenticular autostereoscopic displays are also well-known, with a history that extends back at least 100 years. Miniature and head mounted displays (HMDs) are also well known and may involve a miniaturized version of the planar display technologies. In recent years, stereoscopic or 3D displays, which display a spatially distinct image to each eye, have enjoyed an increasing popularity for applications ranging from fighter pilot helmet displays to virtual reality games. The 3D HMD display technology has numerous extensions including Near-to-Eye (NTD)—periscopes and tank sights; Heads-Up (HUD)—windshield and augmented reality—and immersive displays (IMD)—including CAVE, dome and theater size environments. The principal employed varies little from that of the 1930 Polaroid™ glasses, or the barrier stereoscopic displays of the 1890s, despite. extensive invention related to the active technology to produce each display has occurred over the past twenty years. As applied to small displays, these techniques evolved from miniature cathode ray tubes to include miniature liquid crystal, field emission and other two-dimensional matrix displays, as well as variations of retinal scanning methodologies popularized by Reflection Technologies, Inc. of Cambridge, Mass. in the 1980s. Other approaches include scanning fiber optic point sources such as disclosed by Palmer, U.S. Pat. No. 4,234,788, compact folded, total internal reflection optical displays disclosed by Johnson in U.S. Pat. No. 4,109,263. These inventions have provided practical solutions to the problem of providing lightweight, high resolution displays but are limited to providing a stereoscopic view by means of image disparity. Visual accommodation is not employed. A solution to the problem of accommodation for all displays was disclosed by A. C. Traub in U.S. Pat. No. 3,493,390, Sher in U.S. Pat. No. 4,130,832, and others. These inventors proposed a modulated scanning signal beam coordinated with a resonantly varying focal length element disposed in the optical path between the image display and the observer.
It is well known in the field that wavefront-based technologies, which by definition are limited to coherent effects, impart significant specular and other aberrations degrading performance and inducing observer fatigue.
Alternative approaches where a data-controlled, variable focal length optical element was associated with each pixel of the display were such of experimentation by this inventor and others, including Sony Corporation researchers, in Cambridge, Mass. during the late 1980s. In 1990, Ashizaki, U.S. Pat. No. 5,355,181, of the Sony Corporation, disclosed an HMD with a variable focus optical system.
Despite the improvements during the past decade, the significant problem of providing a low cost, highly accurate visual display with full accommodation remains. One of the principal limitations has been the inability of sequentially resonant or programmed variable focal length optics combined with scanning configurations to properly display solid three dimensional pixels, orthogonal to the scanning plane. Another limitation is the inability of the observer's eye to properly and comfortably focus on rapidly flashing elements. Numerous inventions have been proposed which have generally been too complicated to be reliable, too expensive to manufacture, without sufficient resolution, accuracy, stability to gain wide acceptance. The present invention solves these problems, particularly related to the accurate display of solid and translucent 3D pixels.